Akt-dependent Pp2a activity is required for epidermal barrier formation during late embryonic development

Acquisition of epidermal barrier function occurs late in mouse gestation. Several days before birth a wave of barrier acquisition sweeps across murine fetal skin, converging on dorsal and ventral midlines. We investigated the molecular pathways active during epidermal barrier formation. Akt signaling increased as the barrier wave crossed epidermis and Jun was transiently dephosphorylated. Inhibitor experiments on embryonic explants showed that the dephosphorylation of Jun was dependent on both Akt and protein phosphatase 2A (Pp2a). Inhibition of Pp2a and Akt signaling also caused defects in epidermal barrier formation. These data are compatible with a model for developmental barrier acquisition mediated by Pp2a regulation of Jun dephosphorylation, downstream of Akt signaling. Support for this model was provided by siRNA-mediated knockdown of Ppp2r2a (Pr55α or B55α), a regulatory subunit of Pp2a expressed in an Akt-dependent manner in epidermis during barrier formation. Ppp2r2a reduction caused significant increase in Jun phosphorylation and interfered with the acquisition of barrier function, with barrier acquisition being restored by inhibition of Jun phosphorylation. Our data provide strong evidence that Ppp2r2a is a regulatory subunit of Pp2a that targets this phosphatase to Jun, and that Pp2a action is necessary for barrier formation. We therefore describe a novel Akt-dependent Pp2a activity that acts at least partly through Jun to affect initial barrier formation during late embryonic epidermal development

Management Jobs in the Insurance Industry: Organizational Deskilling and Rising Pay Inequality

The attention of both the research community and the popular press has begun to shift from a traditional focus on production jobs and toward management positions in part because of a perception that a fundamental change is underway in the management ranks. Unlike the temporary layoffs of production workers that were historically driven by business cycles, the changes in management job security seem to be permanent and, in large measure, driven by development inside the firm. The most important of these forces appear to be changes in the structure of management and in the organization of work processes. The authors use a unique set of data to examine the structure of management jobs among a sample of companies and observe how those jobs have changed over time. They examine changes in the skill requirements of jobs by functional area and by level in the organization, changes in the "shape" of the organization chart - the distribution of employees across management job titles - and changes in compensation for these jobs. The data were obtained from Hay Associates, and it included the internal organization of management jobs for 11 life insurance companies. The authors see a sharp expansion in the proportion of line workers, absolute declines in the number of top management positions, and only modest growth in the number of middle managers and supervisors. As a result the organization chart has changed dramatically in these companies, becoming considerably flatter. The "span of control" has increased for every level of the organization and especially for first level management. If the widening of the supervisory span of control resulted from taking decision making and responsibility from supervisors and pushing it down to line workers, it does not seem to have increased the average skill requirements of the exempt line workers. Skill requirements for the other levels rose over the period, especially for top management positions. Overall, the average level of skill in the sample fell substantially between 1986 and 1992 (even though skills rose in two of the four levels) because of a sharp shift in the distribution of employment away from management and toward line positions. The authors suggest that the best description of these patterns is that they represent upskilling of individual jobs and deskilling of organizations. Regarding compensation, none of the levels experienced increases in skill that were statically significant, but top managers received a large (28 percent) increase in pay, middle managers received a modest (10 percent) increase, and the lower two levels received virtually no increases. One conclusion is that earnings inequality is increasing substantially inside these firms in a manner that is not attributable to any increase in skill, and the dividing line for that growth in inequality is no longer exempt/nonexempt but supervisor/manager. A possible explanation for the rising inequality in compensation is that it helps offset change in the probability of promotion. The fact that the span of control is increasing and organizational chart flattening means that the probability of the average worker being promoted is declining. The decline in the probability of promotion might reduce the incentives to work hard. Increases in the compensation of top jobs increase the return to securing a promotion and may offset some of the effect produced by the decline in the probability of promotion. Another explanation is that top mangers are in "better positions to legislate their own pay increases." If true, this sample may actually underrepresent the true extent of income inequality because it consists of companies using an external consultant to help set compensation where internal consistency is an important characteristic of the pay system. These results suggest that "management" as a career will remain attractive, albeit less certain in terms of promotion prospects. Shifts to team-based approaches and the elimination of functional designations would suggest a greater need for generalists than specialists. As technology such as expert systems reduces the need for large units of "experts," the manger's skill will be in recognizing when an expert needs to be called. Leadership skills and the ability to adapt to a changing environment are two qualities that will be sought in the future. Fortunately, these skills will also be useful to team members who are not selected for promotion to mangers. Increasing income inequality may lead to distrust within the organization, though this may be offset by the technical tracks that allow highly skilled non-managers to earn equivalent levels of pay. The fact that insurance companies are relatively unique in facing no major industry-specific shocks from the outside environment suggests that these results should translate well to organizations in other industries.

Reactions at Polymer Interfaces: Transitions from Chemical to Diffusion-Control and Mixed Order Kinetics

We study reactions between end-functionalized chains at a polymer-polymer interface. For small chemical reactivities (the typical case) the number of diblocks formed, $R_t$, obeys 2nd order chemically controlled kinetics, $R_t \sim t$, until interfacial saturation. For high reactivities (e.g. radicals) a transition occurs at short times to 2nd order diffusion-controlled kinetics, with $R_t \sim t/\ln t$ for unentangled chains while $t/\ln t$ and $t^{1/2}$ regimes occur for entangled chains. Long time kinetics are 1st order and controlled by diffusion of the more dilute species to the interface: $R_t \sim t^{1/4}$ for unentangled cases, while $R_t \sim t^{1/4}$ and $t^{1/8}$ regimes arise for entangled systems. The final 1st order regime is governed by center of gravity diffusion, $R_t \sim t^{1/2}$.Comment: 11 pages, 3 figures, uses poliface.sty, minor changes, to appear in Europhysics Letter

The Slowly Formed Guiselin Brush

We study polymer layers formed by irreversible adsorption from a polymer melt. Our theory describes an experiment which is a ``slow'' version of that proposed by Guiselin [Europhys. Lett., v. 17 (1992) p. 225] who considered instantaneously irreversibly adsorbing chains and predicted a universal density profile of the layer after swelling with solvent to produce the ``Guiselin brush.'' Here we ask what happens when adsorption is not instantaneous. The classic example is chemisorption. In this case the brush is formed slowly and the final structure depends on the experiment's duration, $t_{final}$. We find the swollen layer consists of an inner region of thickness $z^* \sim t_{final}^{-5/3}$ with approximately constant density and an outer region extending up to height $h \sim N^{5/6}$ which has the same density decay $\sim z^{-2/5}$ as for the Guiselin case.Comment: 7 pages, submitted to Europhysics Letter

Double Compact Objects III: Gravitational Wave Detection Rates

The unprecedented range of second-generation gravitational-wave (GW) observatories calls for refining the predictions of potential sources and detection rates. The coalescence of double compact objects (DCOs)---i.e., neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS), and black hole-black hole (BH-BH) binary systems---is the most promising source of GWs for these detectors. We compute detection rates of coalescing DCOs in second-generation GW detectors using the latest models for their cosmological evolution, and implementing inspiral-merger-ringdown (IMR) gravitational waveform models in our signal-to-noise ratio calculations. We find that: (1) the inclusion of the merger/ringdown portion of the signal does not significantly affect rates for NS-NS and BH-NS systems, but it boosts rates by a factor $\sim 1.5$ for BH-BH systems; (2) in almost all of our models BH-BH systems yield by far the largest rates, followed by NS-NS and BH-NS systems, respectively, and (3) a majority of the detectable BH-BH systems were formed in the early Universe in low-metallicity environments. We make predictions for the distributions of detected binaries and discuss what the first GW detections will teach us about the astrophysics underlying binary formation and evolution.Comment: published in ApJ, 19 pages, 11 figure